The present invention relates generally to pumps and methods of their construction.
In the past, there has been a need for self-powered pumps which could be used without the presence of a separate power source (such as electricity) to perform certain tasks, including, for example, the injection of additives into gas lines, process tanks, and the like. A style of pump termed a “plunger pump” often has been used for such purposes. One such pump, described as a “fluid operated pump,” is detailed in U.S. Pat. No. 3,093,122, the entire disclosure of which is incorporated herein for all purposes.
Those skilled in the art will ascertain that pumps generally, and plunger pumps in particular, depend on effective sealing members in order to avoid leakage of the material to be pumped. Without proper sealing, the material being pumped can tend to evacuate the pump chamber along the length of the plunger, instead of through the designed exit port. This leakage not only can reduce the efficiency of the pump, it can create maintenance issues and waste a fairly significant amount of the material being pumped. Hence, in the past, and in particular with plunger pumps, a variety of packing materials, including Polytetrafluoroethylene (“PTFE”), perfluoroelastomers (including, for example those commercially available from DuPont Dow Elastomers L.L.C.™ under the trade name KALREZ™), and various other polymers, plastics and the like have been used as sealing members to surround the plunger and prevent leakage of the fluid along the plunger.
Unfortunately, however, in order to adequately seal the plunger from leakage, such packing materials usually must maintain contact with the plunger as it moves reciprocally. The packing materials, therefore, tend to degrade relatively quickly (due at least in part to friction between the plunger, the packing material and/or the fluids being pumped, as well as the expendable nature of the packing materials themselves), allowing progressively more leakage over time. Moreover, as the packing materials degrade, there is a tendency by users to tighten the fitting on such pumps periodically as the packing materials degrade, compressing the packing materials to prevent this progressive leakage, which can significantly impact the efficiency of the pump and require more power for operation. Furthermore, over time, the packing materials can, in fact, score the plunger itself, requiring replacement of the plunger, which can be costly and time consuming. This problem, which can be mitigated, but generally not eliminated, by the use of lubricants to reduce friction, is exacerbated by the fact that such pumps often are used in relatively remote locations because of their desirability as being self-powered, such that they can run unattended for relatively long periods of time. Moreover, the use of lubricants imposes additional maintenance overhead and expense, and it presents the danger that the lubricant might contaminate the material being pumped.
What is needed, therefore, is a new type of sealing member and/or plunger system for such pumps.